Many computer and communication networks being built today, including the Internet, are using fiber optic cabling instead of copper wire. With fiber optic cabling, data is transmitted using light signals, not electrical signals. For example, a logical one may be represented by a light pulse of a specific duration and a logical zero may be represented by the absence of a light pulse for the same duration. The bandwidth of optical fiber is significantly greater than copper since light is attenuated less in fiber than electrons traveling through copper.
While fiber optic cabling is very efficient for transferring data, the use of light signals to process data is still very difficult. For instance, currently there is no efficient way to “store” light signals representative of data. Networks therefore use fiber optics for transmitting data between nodes and silicon chips to process the data within computer nodes. This is accomplished by using fiber optic transceivers, which convert light signals from a fiber optic cable into electrical signals, and vice versa. FIG. 1 illustrates a perspective view of an exemplary optoelectronic module 100 that can be used to form an optical transceiver.
Optoelectronic module 100 includes a semiconductor chip subassembly (CSA) 102 and an optical subassembly (OSA) 104. CSA 102 is a packaged semiconductor device. As shown in FIG. 1, CSA 102 is a rectangular block of molding material 106 that has electrical contacts 108 exposed through its bottom and side surfaces. Within the block of molding material 106 is an encapsulated semiconductor die that is electrically connected to contacts 108. For instance, wire bonds can be used for such connections. Another aspect of CSA 102 that cannot be seen is the up-linking contacts on the top surface of CSA 102. These up-linking contacts are also electrically connected to the encapsulated semiconductor die and therefore provide the electrical communication between the semiconductor die and OSA 104. The specific CSA 102 that is shown is a leadless leadframe semiconductor package (LLP). However, it should be understood that CSA 102 can be formed of various types of molded packages.
OSA 104 is formed of a backing block 110, a circuitry substrate 112, and photonic devices 114. Backing block 110 has a front surface 116 that supports circuitry substrate 112 and photonic devices 114, which are attached to circuitry substrate 112. The backing block 120 can be formed of a variety of materials such as a ceramic material, polyethylene ether ketone (PEEK), or liquid crystal polymer (LCP).
Circuitry substrate 112 is attached to front surface 116 of backing block 110, wraps around the bottom-front corner of backing block 110, and covers most of the bottom surface of backing block 110. Embedded traces within circuitry substrate 112 run from photonic devices 114 on the front surface to the bottom surface of backing block 110 where they make contact with the up-linking contacts of CSA 102. Typically, size dimensions involved with circuitry substrate 112 are very small and cause the circuit traces to be positioned very close to each other. The small size is advantageous in the same way that small sizes for most electronic devices is advantageous. However, the close proximity of the traces cause the problem of “cross-talk,” especially at high operational frequencies. Cross-talk is the electrical interference between two or more electrically conducting elements. Such cross-talk can drastically reduce the performance of optoelectronic device 100.
In view of the foregoing, an efficient technique for connecting the photonic devices of an optical device to a semiconductor chip device that exhibits low levels of cross-talk would be desirable.